Quantum information processing uses quantum mechanical properties to extend the capabilities of information processing. For example, security of information transfer may be enhanced, the amount of information encoded in a communication channel may be increased, and the number of operations required to perform certain computations may be reduced. Just as in conventional information processing where information is stored in one or more bits, quantum information may be stored in one or more quantum bits, known as “qubits.” A qubit may be implemented physically in any two-state quantum mechanical system, such as photon polarization, electron spin, nuclear spin, or various properties of a superconducting Josephson junction, such as charge, energy, or the direction of a current.
Additionally, quantum information may be stored and processed using “qudits,” which are quantum systems with “d” number of discrete quantum states. Qubits are a specific example of a qudit with d=2. Qudits may be implemented using a physical quantum system with multiple states, such as the multiple energy levels of a quantum oscillator.